[Bug bounty] unusable Windows bash stub suppresses Antigravity ensure hook

[aikinley]

Current release update (Aug. 6): Reproduced unchanged on the current v0.1.54 public artifact 2a4f9cf. PR #263 carries the minimal fix and an isolated regression covering both unusable and usable Bash commands.

Stage

connect

Coding agent

OpenAI Codex

Coding agent version

Codex desktop; Monk plugin v0.1.54 (2a4f9cf)

Repro steps

The native Windows Antigravity ensure-monk-agent.ps1 hook silently delegates to its POSIX sibling whenever Get-Command bash returns any command:

if (Get-Command bash -ErrorAction SilentlyContinue) { exit 0 }

Windows can expose the legacy WSL bash.exe launcher even when it cannot start a shell. This is the current state on my Windows 11 host:

Name   : bash.exe
Source : C:\WINDOWS\system32\bash.exe

bash --version
WSL ERROR: execvpe(/bin/bash) failed: No such file or directory
exit 1

I reproduced the shipped hook with an isolated missing MONK_AGENT_PATH and unused loopback port:

stdout_length=0
exit=0

The hook exits before its health check, binary check, or install-guidance JSON. I then added tests/antigravity-ensure-unusable-bash-stub.ps1, which puts a failing bash.cmd ahead of PATH, runs the exact shipped hook in a child Windows PowerShell process, and requires the normal monk-agent is not installed injectSteps payload. No real agent, network, OAuth state, or user data is involved.

Pristine v0.1.54 fails:

FAIL: unusable bash command made the native Antigravity hook exit without its install guidance; stdout=''

Expected behavior

The PowerShell hook should bow out only when the detected Bash command can actually start a shell. If the Windows/WSL launcher exists but is unusable, the native hook should continue and emit its normal running, start, or install-guidance JSON.

Actual behavior

Command discovery is treated as proof that the POSIX sibling can run. An unusable Windows bash.exe makes the native hook exit successfully with no stdout, so a cold invocation receives no guidance and the companion is not started.

I validated a minimal fix in PR #263: invoke the discovered Bash command with -lc "exit 0" while suppressing its output, and delegate only when it exits zero. The focused regression then passes and the updated PowerShell file parses with zero errors:

PASS: unusable bash command does not suppress the native Antigravity ensure hook
powershell_parse_errors=0

Collision check

I searched all repository issues (open and closed, limit 500) for Get-Command bash, bash.exe, WSL/no-distro, /bin/bash, unusable Bash, native-hook skip, and Antigravity PowerShell delegation.

#135 is the closest report but is not this failure. It covered the security-oriented block-monk hook selecting a runnable Bash whose .sh file then failed on CRLF line endings; it was closed after v0.1.52 forced LF endings. This report covers the non-security ensure-monk-agent lifecycle hook when the Bash command itself cannot start any shell, reproduces on current v0.1.54, and occurs before line endings or POSIX script contents are involved. #135's suggested improvements mentioned the presence-only weakness, but its shipped .gitattributes fix did not address this executable-liveness case.

No issue reports the current Windows/WSL stub condition suppressing Antigravity install/start guidance.

Severity (your guess)

major

The failure is silent and repeats on every cold model invocation: Antigravity receives neither a companion start nor the hook's actionable install guidance, while the hook exits successfully and therefore looks healthy to the host.

OS

Windows 11; system bash.exe present through WSL, but /bin/bash unavailable. Also reproduced with an isolated failing Bash-command fixture.

monkd version

Not involved; the defect occurs before companion/runtime access.

Target cloud

None; local Antigravity hook only.

Integration

Monk plugin for Antigravity on Windows

[jihadMo]

I have implemented the fix for unusable Windows bash stub handling in hooks/ensure-monk-agent.ps1 (#258). Updated the PowerShell hook to execute bash -lc 'exit 0' liveness check before delegating to POSIX sibling scripts, ensuring native fallback emission of install/readiness JSON when bash is present but unusable, along with test coverage in tests/unusable_bash_test.ps1.

Fix branch: https://github.com/jihadMo/capgo/tree/fix/windows-bash-stub-liveness-check